The present invention is directed electroplating apparatus, particularly for the electro-deposition of aluminum from an aprotic, oxygen-free and water-free aluminum-organic electrolyte. The apparatus includes an electroplating tank which is closable air-tight and is chargeable with an inert gas above an electrolyte in the tank. The tank has at least one lock for the inward and outward transfer of goods to be electroplated and the lock has at least one lock chamber which is equipped with an inner lock door and an outer lock door and is floodable with an inert gas.
Aluminum deposited from an aprotic, oxygen-free and water-free aluminum-organic electrolyte is distinguished by its ductility, low number of pores, resistance to corrosion and capability of anodic oxidation. Since the presence of air will cause a considerable reduction in the conductivity and in the useful life of this electrolyte due to the reaction with atmospheric oxygen and atmospheric humidity, the electroplating must be undertaken in a treatment apparatus operating under the exclusion of air. In order to prevent the contact of air during inward and outward transfer of the goods, charging and discharging locks are required. These locks are fashioned as gas locks, as liquid locks, and as combined gas-liquid locks and have conveying means for conveying the goods in the lock. German OS No. 27 19 680 discloses an electroplating apparatus for the electro-deposition of aluminum from an aprotic, oxygen-free and water-free aluminum-organic electrolyte, which apparatus has provided a lock chamber which is floodable with inert gas and an antechamber which is also floodable with inert gas so that an inward and outward transfer of goods to be electroplated can occur. The lock is fashioned as a gas lock and is thereby equipped with a total of three lock doors due to the division into the actual lock chamber and into an antechamber. The actual lock chamber is preferably operated with excess pressure so that no disturbing gases or atmospheric humidity can penetrate from the outside into the inert atmosphere which is maintained over the plating bath.
The lock design set forth in the above-mentioned German patent application is not capable of keeping air and humidity away from the electrolyte to an adequate degree. Therefore, it does not suppress the slow decomposition of the electrolyte.
U.S. Pat. No. 4,265,726, whose disclosure is incorporated with reference thereto and which corresponds to European Patent No. 0 013 874, discloses an apparatus for electro-depositing of aluminum wherein a lock system having a liquid lock is employed for the inward and outward transfer of the goods to be electroplated. This liquid lock is provided with an outer lock door and is proceded by an antechamber floodable with inert gas. A penetration of atmosperic oxygen and atmospheric humidity can be considerably reduced with such a lock system in comparison to an exclusive gas lock.
In the electroplating apparatus set forth in the above mentioned patent, the goods to be electroplated are on goods racks, are introduced into the electroplating tank with the assistance of an endless conveyor belt, are introduced from the antechamber floodable with inert gas through the liquid lock and into the plating bath and are then, in turn, transferred out of the electroplating bath in a reversed direction with the assistance of the same conveyor belt. A considerable entrainment of the electrolyte out of the electroplating tank and bath into the liquid lock, however, will occur. Due to the continuous contamination of the fluid of the liquid lock with the electrolyte and the unavoidable reaction with traces of humidity in the antechamber with the inert gas, the device cannot prevent reaction products from being formed and settling onto the clean goods during charging and preventing a subsequent deposition of a technically useable aluminum coatings.
In U.S. Pat. No. 4,363,712, whose disclosure is incorporated by reference and which corresponds to European Patent No. 0 053 676, an apparatus for electro-deposition of aluminum is disclosed. In this apparatus, a contamination of the pretreated goods to be electroplated is prevented in a liquid lock because a separate charging lock composed of an antechamber, liquid lock and a main chamber is separate from a discharging lock which, likewise, has an antechamber, liquid lock and main chamber.
It has turned out in practice that the certain qualities of atmospheric oxygen and atmospheric humidity will enter into the electroplating bath even given locks composed of an antechamber, liquid lock, and main chamber. This is because of entrainment of the oxygen and humidity with the goods to be electroplated into the electroplating bath and also occurs because of the continuous opening and closing of the lock doors. A certain reduction in the conductivity and in the useful life of the electrolyte will occur because of this contamination.